1. Field of the Invention
Methods consistent with the present invention relate to splicing a bend-optimized optical fiber, and more particularly, to heating a bend-optimized fiber before splicing the fiber by analyzing a cold image of the fiber.
2. Description of the Related Art
A related art bend-optimized optical fiber includes a core that is surrounded by a cladding. A mesh of nanometer-scale pockets is infused in the cladding to serve as a barrier that guides light back into the core when the fiber is bent with a very small bending radius, such as 1 cm. This bend-optimized optical fiber solves historic technical challenges related to installing fiber-to-the-home (FTTH) networks in high-rise apartment buildings and condominium complexes. The bend-optimized optical fiber prevents signal loss when bent around corners and routed through a building, enabling telecommunications carriers to install optical fiber cable into these complex environments and provide their customers with the near-infinite bandwidth benefits of a true FTTH solution.
In order to connect two standard optical fibers with each other, the end of each fiber may be heated, so that the fiber ends melt together and form one continuous waveguide. For splicing single mode optical fibers with a large core-to-cladding concentricity error, it is important to use a core alignment method to reduce the splice loss. In a core alignment method, the cores of the fibers are aligned with each other before the fiber ends are melted.
There are several known methods for performing this core alignment before fusion splicing the fibers. For example, many automatic fusion splicers use an image profile alignment system (PAS) that is based on cold fiber image analysis. In the PAS method, either the core or the cladding can be aligned to minimize the splice loss. The PAS method typically achieves a fusion splice loss of approximately 0.03 dB for eccentric fibers.
Another core alignment method is a light injection and detection system (LIDS), in which light is injected into one fiber and detected in the other fiber to be spliced. In addition, active light intensity feedback has been used as a core alignment method. This method uses measurement equipment, such as power meters and optical time domain reflectometers (OTDRs), to align the cores.
Another core alignment method is based on warm splice imaging, in which a fiber is briefly heated to cause the fiber to emit light, and an image of the light emitted from an end of the fiber is recorded. As described in WO 2008/055957, this warm splice imaging method has been used to align the cores of the bend-optimized fibers described above. In the warm splice imaging method, the holes within the cladding are collapsed during the short heating period, which appears to prevent the holes from disturbing the emission of light from the fiber.
The nanometer-scale pockets in the cladding of the bend-optimized fibers render the fiber core invisible during alignment with the PAS method. This makes it impossible to use the PAS method to splice a bend-optimized optical fiber. However, as discussed above, the PAS method can advantageously achieve a fusion splice loss of about 0.03 dB Therefore, a method is needed to enable core alignment of bend-optimized fibers with the PAS method.